A network is a system that allows communication between members of the network. Wireless networks allow such communications without the physical constraints of cables and connectors. Recently, wireless local area networks (a local area network is a computer network covering a local area such as an office or a home) with ranges of about 100 meters or so have become popular. Wireless local area networks are generally tailored for use by computers, and as a consequence such networks provide fairly sophisticated protocols for establishing and maintaining communication links.
The Open Systems Interconnection (OSI) reference model is a standard reference model for communication between end users in a communications network. The OSI reference model has seven layers, the physical, data-link, network, transport, session, presentation, and application layers. The IEEE 802.xx wireless network standards are just a few examples of industry communications standards that have been based on the OSI reference model.
In general terms, the data link layer and the physical layer are directly involved in characterizing a communications channel. The data-link layer handles communications initialization, error checking, and flow control, which are part of a defined Media Access Control (MAC) protocol. The data-link layer exchanges MAC protocol data units (MPDUs) with the physical layer. The MPDUs are frames that may include payload data, headers for a protocol from various higher layers and a frame checksum.
The physical layer is responsible for transmitting and receiving digital information via the physical transport medium (e.g., in a wireless network, high frequency electromagnetic signals serve as the physical transport medium). The physical layer is often subdivided into the physical medium dependent (PMD) sublayer and the physical layer convergence procedure (PLCP) sublayer. The PMD sublayer handles the conversion requirements specific to the physical transport medium. The PLCP sublayer accepts from the data link layer MPDUs to be transmitted, and provides to the data-link layer MPDUs that it has received.
The PLCP sublayer extends MPDUs to be transmitted with information germane to their transport, and extracts MPDUs from received data. Referring now to FIG. 1, the frames transmitted and received by the PLCP layer may include a PLCP preamble 110, a PLCP header 120, and a MPDU 130, which together may be called a PPDU 100 (PLCP Protocol Data Unit).
System designers are working to enhance wireless network performance. One proposed standard involves the use of multiple antennas to increase channel diversity (and thereby increase performance). However, the designers wish to maintain backwards compatibility with existing single-antenna systems. It is thus desirable to implement a convenient way to determine channel estimation from a received transmission using multiple antennas while maintaining backward compatibility with single antenna systems.